Lubrication of mandrels for tube extrusion



Oct. 20, 1964 B. J. BUNTZ ETAL 3,153,482

LUBRICATION OF MANDRELS F OR TUBE EXTRUSION Filed June ll, 1963 Wig-1IEE-E INVETORS ,Bal/ze Z ,Panty [eBsYer-A? Zif/fiefasall M Q. www

Kto/'Wg United States Patent O M 3,153,482 LUBRICATION OF MANDRELS FORTUBE EXTRUSION Billie J. Kuntz, Cushing, Okla., and Lester A.Unnerstall,

Washington, Mo., assignors, by mesne assignments, to

the United States of America as represented by the United States AtomicEnergy Commission Filed .lune 11, 1963, Ser. No. 287,161 2 Cls. (Cl.207-3) This invention relates to the lubrication of a piercing mandrelused in the extrusion of tubing.

In the extrusion art difficulty is often experienced in centering apiercing mandrel accurately in an extrusion die. An inadequatelysupported mandrel causes variations in tubing wall thickness. This isreferred to as a lack of concentricity. Such variations frequentlyamount to 10 percent of the wall thickness.

It is important in tubular nuclear fuel elements such as those describedin U.S. Patent No.72,992,172, issued July 1l, 1961, to have uniformtubing wall thickness both for uniform heat generation and for uniformtransfer of heat to cooling mediums. Extrusions that yield tubing closerto the final machined dimensions are an advantage in that a higherpercentage of the tubing will meet strict specilications foracceptability.

Another diiiculty has been that of providing adequate lubrication forthe mandrel surfaces which come into contact with a hot billet. Normallya piercing mandrel is lubricated after it passes through its lastsupport, which is at some distance from the piercing end of the mandrel.If the support is placed close to the piercing end of the mandrel, theonly lubricant on the mandrel is that which passes through the support.Lubrication provided in this manner is inadequate if the support titsthe mandrel closely enough to accurately maintain the position of themandrel in the extrusion die. Mandrel replacement is costly, yet if notreplaced, a Worn mandrel causes inferior inside surface finish in theextruded tubing.

The present invention has resulted in a substantial improvement inconcentricity of extruded uranium tubing so that variations inconcentricity are consistently less than percent of the tubing wallthickness and are usually in the neighborhood of 3 percent. In addition,mandrel life has been increased by at least a factor of l0 with anassociated improvement in smoothness of the inside surfaoes of thetubing.

This has been accomplished by the present invention which includesiilling a piercing cap with lubricant and providing a lubricant wellaround the mandrel just ahead of a guide bearing positioned close to thebillet so that as the mandrel is driven forward the lubricant is forcedback into the lubricant well thereby lubricating the mandrel after themandrel passes through the guide bearing.

It is an object of this invention to minimize variations in tubingconcentricity.

It is also an object of this invention to increase mandrel life.

It is a further object of this invention to maintain uniform quality ofinner surface smoothness in extruded tubing.

Other advantages of the present invention will be apparent from thefollowing description and accompanying drawing in which:

PIG. 1 is a sectional view taken in elevation of an extrusion set-uppreliminary to a piercing operation.

FIG. 2 is a similar view after piercing showing the be ginning of anextrusion operation.

A piercing mandrel is centered in a tubular extrusion ram 12 by asupport sleeve 14 which is carried by the forward end 16 of the ram 12.The support sleeve 14 has a guide bearing portion 18 in close-fittingcontact 3,153,482v Patented Oct. 20, 1964 ICC with the mandrel 10. Arecess 20 in the forward end of the support sleeve 14 receives apiercing cap 22 which, according to this invention, has been iilled withlubricant 24. Between the recess 20 and the bearing portion 18 Vis alubricant well 26 which receives the lubricant as it is displaced fromthe piercing cap` 22 by the piercing end 28 of the mandrel 10 as themandrel moves forward.

The lubricant may be one of several commonly used `types of extrusionlubricant for high temperature use.

The lubricant should be Viscous enough to be retained in the lubricantwell 26 and to adhere to the surface of the mandrel 1t? under operatingconditions. Grease-base extrusion lubricants containing graphite oraluminum flake are satisfactory, for example, in gamma phase extrusion`of uranium.

`is press-fitted into a die case 36.

As the ram 12 is driven forward the billet 32 is upset to fill a cavity38 between the die case 36 and a forward face 40 of the dummy block 30,a forward end 42 of the support sleeve 14 and the piercing cap 22. Then,the mandrel 10 is driven through the billet 32 carrying the piercing cap22 with it until the piercing end 2S of the mandrel 10 extends beyondthe die insert opening 34 where the cap 22 ilies off. The mandrel 10 inpassing through the lubricant-lilled Well 26 picks up lubricant on itslateral surfaces. The amount of lubricant fed into the lubricant wellmay be controlled by varying the amount of lubricant placed in thepiercing cap prior to extrusion.

As the ram 12 moves forward, it upsets the billet 32, causing the billetmetal to close in around the mandrel 10 as the billet material begins toextrude through the die insert opening 34 as shown in FIG. 2. Thelubricant 24 adheres to the surface of the mandrel out of direct contactwith hot billet material until the extrusion operation is under way.This facilitates horizontal extrusion operations which are difficult inmethods where a fluid lubricant such as molten glass is applied to thesurface of the hot billet metal itself.

If a mandrel is lubricated before it is driven through the close-fittingguide bearing portion 18, the residual lubricant left on the mandrel isnot adequate to protect the mandrel from erosion by the hot metal. Undersuch conditions a mandrel used for extruding uranium tubing lasts foronly about fifteen billets. On the other hand we have found that amandrel lubricated according to this invention will still be suitablefor use after extruding several hundred billets. This represents aconsiderable saving in mandrel replacement costs. It also represents agreat improvement in uniformity of the inside diameter of the extrudedtubing as well as in smoothness of the inside surface of the tubing.

In gamma phase extrusion of uranium we have found hot work tool steelssuch as A.I.S.I. Hll and H12 to be satisfactory for extrusion equipmentwhich comes into contact with hot uranium billets. For the die insert35, high speed tool steel such as A.I.S.I. T1 has proven satisfactory.The support sleeve 14 was made of A.I.S.I. H13, a hot work tool steel.

This invention is not limited to the exact details disclosed, but may beembodied in other forms within the scope of the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A tube extrusion apparatus comprising: a die case 3 having a cavityadapted to receive a billet of a material to be extruded, said die casehaving an extrusion opening in one face thereof through which saidmaterial may be extruded; a tubular ram positioned to axially enterv thecavity in said dieA case essentially in axial alignment with saidextrusion opening; a piercing mandrel extending axially through thetubular ram and adapted to be extended forward through the billet andinto the extrusion opening, said mandrel being smaller in diameter thanYthe diameter of the extrusion opening; a piercing cap adapted to t overa forward end of said mandrel; a support sleeve positioned in a forwardend of the ram and rigidly supported thereby, said sleeve having arearwardly positioned guide-bearing portion snugly receiving `saidpiercing mandrel, said sleeve having a recess in a forward end thereofin axial alignment with said guide-bearing portion adapted to receivethe piercing cap, said sleeve having a lubricant well between theguide-bearing portion and the said recess, said Wellv being disposedabout the mandrel in a lubricant-applying relationship thereto and beingof a size suliicient to receive lubricant displaced from the piercingcap as the mandrel is driven forward; and a dummy block positionedbetween the forwardend of the ram and the billet, said dummy block beingcentered around and supported by a forward portion of said supportsleeve, said dummy block having a forward face essentially in the sameplane as the plane of the forward end of the support sleeve.

2. A device for centering and lubricating a piercing mandrel in a tubingextrusion die, comprising: a support sleeve carried by and centered in aforward end of an extrusion ram, said sleeve having a rearwardlypositioned guide-bearing portion snugly receiving said piercing mandrel,said sleeve having a recess in a forward end in axial alignment withsaid guide-bearing portion and adapted to receive a piercing cappositioned over a forward en-d of the piercing mandrel, said sleevehaving a lubricant well positioned between said recess and said guidebearing portion, said wellbeingdisposed about lsaid piercing mandrel ina lubricant-applying relationship thereto, said well being of a sizesuicient to receive at least a major portion of 'a lubricantA displacedfrom a lubricant-filled piercing cap as the mandrel is driven forwardthrough a billet to be extruded.

1. A TUBE EXTRUSION APPARATUS COMPRISING: A DIE CASE HAVING A CAVITYADAPTED TO RECEIVE A BILLET OF A MATERIAL TO BE EXTRUDED, SAID DIE CASEHAVING AN EXTRUSION OPENING IN ONE FACE THEREOF THROUGH WHICH SAIDMATERIAL MAY BE EXTRUDED; A TUBULAR RAM POSITIONED TO AXIALLY ENTER THECAVITY IN SAID DIE CASE ESSENTIALLY IN AXIAL ALIGNMENT WITH SAIDEXTRUSION OPENING; A PIERCING MANDREL EXTENDING AXIALLY THROUGH THETUBULAR RAM AND ADAPTED TO BE EXTENDED FORWARD THROUGH THE BILLET ANDINTO THE EXTRUSION OPENING, SAID MANDREL BEING SMALLER IN DIAMETER THANTHE DIAMETER OF THE EXTRUSION OPENING; A PIERCING CAP ADAPTED TO FITOVER A FORWARD END OF SAID MANDREL; A SUPPORT SLEEVE POSITIONED IN AFORWARD END OF THE RAM AND RIGIDLY SUPPORTED THEREBY, SAID SLEEVE HAVINGA REARWARDLY POSITIONED GUIDE-BEARING PORTION SNUGLY RECEIVING SAIDPIERCING MANDREL, SAID SLEEVE HAVING A RECESS IN A FORWARD END THEREOFIN AXIAL ALIGNMENT WITH SAID GUIDE-BEARING PORTION ADAPTED TO RECEIVETHE PIERCING CAP, SAID SLEEVE HAVING A LUBRICANT WELL BETWEEN THEGUIDE-BEARING PORTION AND THE SAID RECESS, SAID WELL BEING DISPOSEDABOUT THE MANDREL IN A LUBRICANT-APPLYING RELATIONSHIP THERETO AND BEINGOF A SIZE SUFFICIENT TO RECEIVE LUBRICANT DISPLACED FROM THE PIERCINGCAP AS THE MANDREL IS DRIVEN FORWARD; AND A DUMMY BLOCK POSITIONEDBETWEEN THE FORWARD END OF THE RAM AND THE BILLET, SAID DUMMY BLOCKBEING CENTERED AROUND AND SUPPORTED BY A FORWARD PORTION OF SAID SUPPORTSLEEVE, SAID DUMMY BLOCK HAVING A FORWARD FACE ESSENTIALLY IN THE SAMEPLANE AS THE PLANE OF THE FORWARD END OF THE SUPPORT SLEEVE.